A self-transmissible, narrow-host-range endogenous plasmid of Rhodobacter sphaeroides 2.4.1: physical structure, incompatibility determinants, origin of replication, and transfer functions.
A self-transmissible, narrow-host-range endogenous plasmid
of Rhodobacter sphaeroides 2.4.1: physical structure,
incompatibility determinants, origin of replication, and
transfer functions.
A Suwanto and S Kaplan
Department of Microbiology and Molecular Genetics, University of Texas Health Science
Center, Houston 77225.
Abstract
Rhodobacter sphaeroides 2.4.1 naturally harbors five cryptic endogenous plasmids (C. S.
Fornari, M. Watkins, and S. Kaplan, Plasmid 11:39-47, 1984). The smallest plasmid (pRS241e),
with a molecular size of 42 kb, was observed to be a self-transmissible plasmid which can
transfer only to certain strains of R. sphaeroides. Transfer frequencies can be as high as 10(-2) to
10(-3) per donor under optimal mating conditions in liquid media in the absence of oxygen.
pRS241e, designated the S factor, was also shown to possess a narrow host range, failing either
to replicate or to be maintained in Escherichia coli, Agrobacterium tumefaciens, and Rhizobium
meliloti. It was further revealed that one of the remaining four endogenous plasmids, pRS241d,
was also transmissible at a frequency similar to that of the S. factor. As a cointegrate with
pSUP203, S was maintained in E. coli, providing sufficient DNA from which a physical map of
S could be constructed. Progressive subcloning of S-factor DNA, in conjunction with assays of
plasmid transfer, led to the localization and identification of oriV (IncA), IncB, and the putative
oriT locus. The DNA sequence of the 427 bp containing oriTs revealed topological similarity to
other described oriT sequences, consisting of an A-T-rich DNA region, several direct and
inverted repeats, and putative integration host factor (IHF)-binding sites, and was shown to be
functional in promoting plasmid transfer.
http://jb.asm.org/cgi/content/abstract/174/4/1124
of Rhodobacter sphaeroides 2.4.1: physical structure,
incompatibility determinants, origin of replication, and
transfer functions.
A Suwanto and S Kaplan
Department of Microbiology and Molecular Genetics, University of Texas Health Science
Center, Houston 77225.
Abstract
Rhodobacter sphaeroides 2.4.1 naturally harbors five cryptic endogenous plasmids (C. S.
Fornari, M. Watkins, and S. Kaplan, Plasmid 11:39-47, 1984). The smallest plasmid (pRS241e),
with a molecular size of 42 kb, was observed to be a self-transmissible plasmid which can
transfer only to certain strains of R. sphaeroides. Transfer frequencies can be as high as 10(-2) to
10(-3) per donor under optimal mating conditions in liquid media in the absence of oxygen.
pRS241e, designated the S factor, was also shown to possess a narrow host range, failing either
to replicate or to be maintained in Escherichia coli, Agrobacterium tumefaciens, and Rhizobium
meliloti. It was further revealed that one of the remaining four endogenous plasmids, pRS241d,
was also transmissible at a frequency similar to that of the S. factor. As a cointegrate with
pSUP203, S was maintained in E. coli, providing sufficient DNA from which a physical map of
S could be constructed. Progressive subcloning of S-factor DNA, in conjunction with assays of
plasmid transfer, led to the localization and identification of oriV (IncA), IncB, and the putative
oriT locus. The DNA sequence of the 427 bp containing oriTs revealed topological similarity to
other described oriT sequences, consisting of an A-T-rich DNA region, several direct and
inverted repeats, and putative integration host factor (IHF)-binding sites, and was shown to be
functional in promoting plasmid transfer.
http://jb.asm.org/cgi/content/abstract/174/4/1124